Placental vascular morphogenesis

Appropriate growth and development of the placenta is essential for fetal g rowth and wellbeing, and indeed may be an important factor in determining a dult health.(1) As the fetus grows its demands increase and the capacity of the placenta to facilitate transfer between the fetal and maternal circula tions increases as gestation progresses. The principal units for diffusiona l exchange of oxygen are the terminal villi, and these develop in the third trimester. It is thought that capillary growth within the villi drives the growth of these structures which are characterized by a high proportion of their volume being occupied by fetal capillaries and extreme thinning of t he trophoblast and endothelial cell layers. In the first trimester the PO i n the intervillous space is low and rises sharply at the start of the secon d. Endothelial growth is influenced by a variety of soluble factors, and se veral of these are regulated by oxygen, for example, vascular endothelial g rowth factor (VEGF), angiopoietin 2, and soluble fit (a VEGF antagonist). T hus, fetal demand may regulate villous growth and differentiation by alteri ng local PO2 which, in turn, modulates growth factors (or their antagonists ) to regulate endothelial growth and vessel re-modelling.